Twilight Sparkle is Princess Celestia's most faithful student. She's learned many things under Celestia's tutorship; magic, friendship, happiness, and many more. But she's also made a lot of simple mistakes.

Celestia thought that Twilight would be ready to complete Starswirl the Bearded's unfinished spell. It was one of the only spells that would turn somepony into an alicorn that she knew of. But she didn't expect this.

Now, after a magical mishap, everyone in Equestria has turned into an Alicorn.

What could possibly go wrong with that?